<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>躁动的心</title>
    <style>
        header{
            width: 100px;
            height: 100px;
            margin:200px auto;
            background-color: red;
            position: relative;
            transform: rotate(45deg);
            z-index: 1;
            animation: 2s spin steps(2,end) infinite;
        }
        .a{
            width: 100px;
            height: 100px;
            background-color: red;
            border-radius: 50%;
            z-index: 3;
            position: absolute;
            top:-50%;
            left: 0;
            animation: 2s spin steps(2,end) infinite;
        }
        .b{
            width: 100px;
            height: 100px;
            background-color: red;
            border-radius: 50%;
            z-index: 2;
            position: absolute;
            right: 50%;
            top: 0;
            animation: 2s spin steps(2,end) infinite;
        }
        @keyframes spin {
            0%{
                width: 100px;
                height: 100px;
            }
            50%{
                width: 120px;
                height: 120px;
            }
            100%{
                width: 150px;
                height: 150px;
            }
        }
    </style>
</head>
<body>
<header>
    <div class="a"></div>
    <div class="b"></div>
</header>
</body>
</html>